1. Field of the Invention
The present invention relates generally to a claw-pole type stepping motor, and more particularly to a stator structure of that motor.
2. Description of the Related Art
FIG. 1 is a partly cut-away perspective view of a claw-pole type stepping motor with a conventional stator structure.
Referring to FIG. 1, the claw-pole type stepping motor comprises mainly a stator assembly 9 consisting of a pair of stator subassemblies 8 which are put together back-to-back against each other, and a rotor 11 disposed rotatably inside the stator assembly 9.
A front plate 10a and a rear plate 10b are fitted to the stator assembly 9. A shaft 12 is press fitted into the rotor 11 and rotatably supported by a bearing 13a disposed on the front plate 10a and by another bearing (not shown) disposed on the rear plate 10b. 
FIGS. 2A and 2B show the structure of each of the stator subassemblies 8 making up the conventional stator assembly 9, in which FIG. 2A is an exploded view of each of the stator subassembies and FIG. 2B is an assembled view thereof.
As shown in FIG. 2A, the stator subassembly 8 primarily comprises: an outer stator yoke 1 having a plurality of pole teeth 6a which are blanked out and bent by 90xc2x0 along the circumferential surface of the central portion of the circular sidewall of a cup-shaped or cylindrical member made of a soft magnetic steel plate formed by deep drawing; an inner stator yoke 2 having a plurality of pole teeth 6b which are blanked out and bent by 90xc2x0 along the circumferential surface of the central portion of substantially circular member made of a soft magnetic steel plate; a coil 3 which is prepared by winding a magnet wire around a bobbin 4; and a covering 5 which covers the coil 3.
The stator subassembly 8 is formed as shown in FIG. 2B by combining the outer stator yoke 1 with the inner stator yoke 2 such that their respective plurality of pole teeth 6a and 6b are intermeshed with each other with a gap therebetween, and are misaligned from each other by an electrical angle of 180xc2x0, mounting the coil 3 and the covering 5, and filling the gap between the respective plurality of pole teeth 6a and 6b with resin.
The stator assembly 9 (see FIG. 1) is formed by coupling together two stator subassemblies 8 back-to-back such that the respective plurality of pole teeth 6a and 6b of the two stator subassemblies 8 are misaligned from each other by an electrical angle of 90xc2x0.
The conventional stator assembly 9 formed as above poses the following problems.
In the claw-pole type stepping motor having the stator assembly 9, an external wall 7 of the outer stator yoke 1 extends along the overall perimeter. Accordingly, throughout the perimeter of the stator assembly 9, the external dimensions include the dimension corresponding to double the plate thickness of the soft magnetic steel plate, which is the material of the external wall 7, i.e., the material of the outer stator yoke 1. This impedes the size reduction.
Especially, in the event of use in notebook computers needing a reduced thickness, the height is strictly limited as compared with the other dimensions, while higher performances are demanded. This means that even the plate thickness of the outer stator yoke 1 can constitute a serious obstacle.
Furthermore, since the outer periphery of the cup-shaped or cylindrical outer stator yoke is formed by deep drawing, the press working is difficult and the press die is expensive, thereby causing the manufacturing costs to increase.
The present invention was conceived in view of the above circumstances involved in the related art. It is therefore an object of the present invention to provide a claw-pole type stepping motor capable of achieving a miniaturization and reducing the manufacturing costs, without impairing the motor performances.
In order to attain the above object, according to a primary aspect of the present invention there is provided: a stator structure of a claw-pole type stepping motor having a rotor disposed inside and rotatable relative to the stator, comprising an outer stator yoke having a plurality of pole teeth; an inner stator yoke having a plurality of pole teeth which are intermeshed with the plurality of pole teeth of the outer stator yoke with a gap therebetween; a coil disposed around the circumferential periphery defined by the intermeshed pole teeth; and a covering which covers the coil; wherein stator external walls are partially formed so as to allow the covering to be exposed in regions where the stator external walls are not formed.
The stator structure of a claw-pole type stepping motor according to the primary aspect has the following subsidiary aspects.
The stator external walls are formed by bending extended portions formed at both ends of a main plate portion of the inner stator yoke.
The stator external walls are formed by bending extended portions formed at both ends of a main plate portion of the outer stator yoke.
The stator external walls are formed by bending extended portions formed at both ends of a main plate portion of the inner stator yoke and also by bending extended portions formed at both ends of a main plate portion of the outer stator yoke.
Each of the main plate portions of the outer stator yoke and the inner stator yoke is rectangular in shape.
Each of the main plate portions of the outer stator yoke and the inner stator yoke is ellipsoidal in shape.
In the present invention, as is apparent from the aspects set forth hereinabove, the periphery of the coil i.e. the covering, is partly covered by the external walls extending from the stator yoke so that exposed regions can produce dimensional reduction by the thickness dimension of the stator yoke material. Specifically, the dimensional reduction corresponds to double the thickness of the stator yoke material. On the other hand, the dimensions of the coil, rotor, etc. are not influenced at all, with the result that the motor performances will by no means be sacrificed in exchange for the miniaturization. Thus, this is very effective in satisfying the demand for higher performances as well.
When the same external dimensions are allowed as those of the motor having the conventional stator structure, it will be easier to secure the space for the coil than conventionally, thus making it easier to increase the inner diameter of the circumference defined by the pole teeth and the rotor diameter and, as a result, to provide a higher-torque motor at a reduced cost.
In addition, since the stator yoke member is not cup shaped or cylindrical, there is no need for deep drawing. This makes it possible to pick up the manufacturing work speed, lower the die cost and improve its durability, thus achieving a reduction in the manufacturing cost. In addition, since the stator yoke material is consumed in a reduced amount, the manufacturing cost can be further reduced, and also the natural resources can be saved, which is advantageous in terms of environmental protection.
In this connection, the main plate portion of the outer stator yoke can be rectangular, ellipsoidal or of any other shapes depending on the space to be allowed.
The above and many other objects, aspects, features and advantages of the present invention will become more apparent to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative examples.